Legionella in Drinking Water
Complete contaminant profile for Legionella bacteria, including sources, health risks, transmission pathways, testing methods, treatment technologies, building water systems, and drinking water safety guidance.
Quick Facts
What Is Legionella?
Legionella is a group of bacteria naturally found in freshwater environments such as rivers, lakes, and streams. Problems occur when Legionella enters human-made water systems and multiplies under favorable conditions.
The bacteria are best known for causing Legionnaires’ disease, a potentially serious form of pneumonia, and Pontiac fever, a milder flu-like illness.
Why Legionella Matters
Unlike many drinking water contaminants, Legionella is usually not transmitted by drinking water itself. Instead, infection occurs when contaminated water droplets are inhaled into the lungs.
Main Sources of Legionella Contamination
Hot Water Systems
Warm water temperatures can encourage Legionella growth if systems are not properly maintained.
Cooling Towers
Cooling towers have been associated with numerous Legionella outbreaks worldwide.
Showers and Faucets
Water droplets generated by showers and faucets can become transmission pathways.
Stagnant Plumbing
Unused pipes, low-flow sections, and dead-end plumbing can create favorable growth conditions.
Potential Health Concerns
Legionnaires’ Disease
A severe form of pneumonia that may require hospitalization and can be life-threatening in vulnerable individuals.
Pontiac Fever
A milder illness that resembles influenza and generally resolves without serious complications.
High-Risk Populations
Older adults, smokers, individuals with chronic lung disease, hospitalized patients, and immunocompromised individuals face greater risk.
How Exposure Occurs
- Shower aerosols
- Cooling tower mist
- Decorative fountains
- Hot tubs and spas
- Humidifiers
- Large building plumbing systems
Drinking contaminated water is generally not considered the primary transmission route.
Regulatory and Monitoring Status
| Authority | Status | Use for Readers |
|---|---|---|
| CDC | Major public health concern | Understand outbreak prevention and response |
| WHO | Building water safety guidance | Review international risk management practices |
| Local Health Authorities | Building-specific oversight | Follow outbreak notices and guidance |
How Legionella Is Detected
- Culture testing
- PCR analysis
- Water system monitoring programs
- Environmental sampling
- Building risk assessments
Legionella Control Methods
| Control Method | Effectiveness | Notes |
|---|---|---|
| Temperature Management | Excellent | One of the most important control strategies |
| Chlorination | High | Common water system disinfection method |
| Chlorine Dioxide | High | Frequently used in large facilities |
| Copper-Silver Ionization | High | Often used in hospitals and large buildings |
| UV Disinfection | Moderate to High | Useful as part of a broader control program |
Building Water System Risk Factors
Legionella thrives in warm, stagnant water. Risk increases when plumbing systems are poorly maintained, water temperatures are favorable, or disinfectant levels are insufficient.
Large and complex plumbing systems are generally more difficult to manage.
Recommended Prevention Strategy
- Maintain appropriate hot water temperatures.
- Flush rarely used outlets.
- Inspect cooling towers regularly.
- Implement water management programs.
- Monitor disinfectant levels.
- Test high-risk facilities when appropriate.
Travel and Hotel Considerations
Travelers may encounter Legionella exposure in hotels, cruise ships, resorts, spas, and large buildings. Facilities with robust water management programs generally reduce risk.
This is one reason why water safety information is valuable for international travelers.
Related Contaminants
Frequently Asked Questions
Can I get Legionella from drinking water?
Inhalation of contaminated water droplets is the primary exposure route.
Where is Legionella most commonly found?
Building plumbing systems, hot water systems, cooling towers, spas, and decorative fountains.
Can boiling water kill Legionella?
High temperatures can destroy Legionella, which is why temperature management is an important control strategy.
Who is most at risk?
Older adults, smokers, hospitalized patients, and immunocompromised individuals.
Can Legionella grow in home plumbing?
Yes, especially in warm stagnant water systems.
Authority Sources
Quick Summary
Legionella is a bacterial contaminant primarily associated with building water systems rather than source water itself. It can cause Legionnaires’ disease and other illnesses when contaminated water droplets are inhaled. Effective prevention relies on temperature control, disinfection, system maintenance, and comprehensive water management programs.